1. Technical Field
The invention relates to apparatus and methods for sensing temperature with an integrated electronic circuit. The temperature sensor and related methods may be used for sensing temperature in a multi-pixel array of an imaging device.
2. Discussion of the Related Art
Solid-state temperature sensors have been developed to be incorporated in electronic and mechanical systems to provide real-time monitoring of system temperature during operation. There are a wide variety of applications in which temperature sensors are used, ranging from environmental sensing and control, cooking devices, medical devices, consumer electronics, and machine diagnostics, control, and safety. As one simple example, temperature sensors can be used as a safety element in some applications, e.g., electrical motors, and provide a signal that will shut off an overheating system to prevent damage to the system.
Some temperature sensors are thermistor based, in which a temperature-sensitive resistor (thermistor) is used in a circuit to sense temperature, as depicted in FIG. 1 for example. The thermistor 110 can be incorporated in a voltage divider (e.g., comprised of resistor Ri and thermistor 110), and an output of the divider Vout can be provided to one input of a differential amplifier 140. A reference voltage Vref may be provided to a second input of the differential amplifier. Since the resistance of thermistor is a function of temperature, Vout will be temperature dependent. Vout will be compared with the constant reference voltage Vref and any deviations in due to temperature changes will be sensed by differential amplifier 140, amplified, and provided as an output voltage VPT that is proportional to temperature.
Though a temperature-sensing circuit such as that shown in FIG. 1 may be used in a large number of applications, it is not suitable for some applications for several reasons. One reason is that it can consume too much power for low-power applications, such as cell phones. Another reason is that it requires at least one stable and temperature-independent voltage source. Another reason is that it generally comprises large circuit elements that are not well suited for integration into micro-circuits. Also, calibration of the sensor requires control of a reference voltage source, Vref. Additionally, if the thermistor 110 is large, the temperature response of the circuit may be slow for some applications (e.g., sensing heating due to electrical power surges).